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1. Synthesis and Li-ion electrode properties of layered MAB phases Ni n+1 ZnB n ( n = 1, 2)

   https://doi.org/10.1039/c9ta12937e  

   Rezaie, Amir A. ; Yan, Zheng ; Scheifers, Jan P. ; Zhang, Jian ; Guo, Juchen ; Fokwa, Boniface P. ( January 2020 , Journal of Materials Chemistry A)

   null (Ed.)

   Ternary MAB phases (layered transition metal borides) have recently attracted interest due to their exfoliation potential toward MBenes (analogous to MXenes), which are predicted to have excellent Li-ion battery performance. We have achieved single-phase synthesis of two MAB phases with general composition Ni n+1 ZnB n ( n = 1, 2), the crystal structures of which contain zinc layers sandwiched between thin ( n = 1) and thick ( n = 2) Ni–B slabs. Highly stacked MAB sheets were confirmed by X-ray diffraction and high-resolution scanning electron microscopy for both materials. Exposing Ni n+1 ZnB n to diluted hydrochloric acid led to the creation of crystalline microporous structures for n = 1 and non-porous detached sheets for n = 2. Both morphologies transformed the inactive bulk materials into highly active Li-ion battery anodes with capacities of ∼90 mA h g −1 ( n = 1) and ∼70 mA h g −1 ( n = 2) at a 100 mA g −1 lithiation–delithiation rate. The XPS analysis and BET surface area measurements reveal that the increased surface area and the reversible redox reaction of oxidized nickel species are responsible for this drastic increase of the lithiation–delithiation capacity. This proof of concept opens new avenues for the development of porous MAB, MAB nanosheets, MBenes and their composites for metal-ion battery applications. 

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2. Oxygen Incorporation in the Molecular Beam Epitaxy Growth of Sc x Ga 1−x N and Sc x Al 1−x N

   https://doi.org/10.1002/pssb.201900612  

   Casamento, Joseph ; Xing, Huili Grace ; Jena, Debdeep ( January 2020 , physica status solidi (b))

   Secondary‐ion mass spectrometry (SIMS) is used to determine impurity concentrations of carbon and oxygen in two scandium‐containing nitride semiconductor multilayer heterostructures: Sc_xGa_1−xN/GaN and Sc_xAl_1−xN/AlN grown by molecular beam epitaxy (MBE). In the Sc_xGa_1−xN/GaN heterostructure grown in metal‐rich conditions on GaN–SiC template substrates with Sc contents up to 28 at%, the oxygen concentration is found to be below 1 × 10¹⁹ cm⁻³, with an increase directly correlated with the scandium content. In the Sc_xAl_1−xN–AlN heterostructure grown in nitrogen‐rich conditions on AlN–Al₂O₃template substrates with Sc contents up to 26 at%, the oxygen concentration is found to be between 10¹⁹and 10²¹ cm⁻³, again directly correlated with the Sc content. The increase in oxygen and carbon takes place during the deposition of scandium‐alloyed layers.

    

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3. Co 2‐x Rh x P Nanoparticles for Overall Water Splitting in Basic Media: Activation by Phase‐Segregation‐Assisted Nanostructuring at the Anode

   https://doi.org/10.1002/cctc.202100483  

   Mutinda, Samuel I. ; Batugedara, Tharanga N. ; Brown, Benjamin ; Brock, Stephanie L. ( August 2021 , ChemCatChem)

   The application of Co_2‐xRh_xP nanoparticles as electrocatalysts for the hydrogen evolution reaction (HER) and overall water splitting in basic media is reported. The experimental design seeks to dilute rhodium with earth‐abundant cobalt as a means to lower the cost of the material and achieve catalytic synergism, as reported for related bimetallic phosphides. The HER activity of Co_2‐xRh_xP is found to be composition‐dependent, with the rhodium‐rich compositions being more active as compared to their cobalt‐rich counterparts, with overpotentials (η) at 10 mA/cm²_geometricof 58.1–63.9 mV vs. 82.1–188.1 mV, respectively. In contrast, Co‐rich Co_2‐xRh_xP nanoparticles are active for the oxygen evolution reaction (OER) process in basic media, with η= 290 mV for x=0.25. A full water electrolysis cell was created using the most active compositions for OER and HER as the anode and cathode, respectively, generating an overall η= 390 mV. Notably, the cell became more active over a 50 h stability test, increasing by 2 mV/cm²_geometricat a constant applied voltage of 1.62 V vs NHE. This enhanced activity correlates with nanoscale phase segregation of Rh in the anode. Thus, the lower overpotential achieved for Co_1.75Rh_0.25P relative to Co₂P, and the augmented activity over time in the former, may be a consequence of restructuring of the anode driven by Rh phase‐segregation. The augmentation in activity at the anode more than compensates for small losses at the cathode.

    

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4. Highly active and stable nickel–molybdenum nitride (Ni 2 Mo 3 N) electrocatalyst for hydrogen evolution

   https://doi.org/10.1039/D0TA10090K  

   Park, Sang Heon ; Jo, Tae Hwan ; Lee, Min Hee ; Kawashima, Kenta ; Mullins, C. Buddie ; Lim, Hyung-Kyu ; Youn, Duck Hyun ( March 2021 , Journal of Materials Chemistry A)

   null (Ed.)

   This paper reports a highly active and stable nonprecious metal electrocatalyst based on bimetallic nanoscale nickel molybdenum nitride developed for the hydrogen evolution reaction (HER). A composite of 7 nm Ni 2 Mo 3 N nanoparticles grown on nickel foam (Ni 2 Mo 3 N/NF) was prepared through a simple and economical synthetic method involving one-step annealing of Ni foam, MoCl 5 , and urea without a Ni precursor. The Ni 2 Mo 3 N/NF exhibits high activity with low overpotential ( η 10 of 21.3 mV and η 100 of 123.8 mV) and excellent stability for the HER, achieving one of the best performances among state-of-the-art transition metal nitride based catalysts in alkaline media. Supporting density functional theory (DFT) calculations indicate that N sites in Ni 2 Mo 3 N with a N–Mo coordination number of four have a hydrogen adsorption energy close to that of Pt and hence may be responsible for the enhanced HER performance. 

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5. Elucidating the Impact of Mg Substitution on the Properties of NASICON‐Na 3+ y V 2− y Mg y (PO 4 ) 3 Cathodes

   https://doi.org/10.1002/adfm.202105463  

   Ghosh, Subham ; Barman, Nabadyuti ; Gonzalez‐Correa, Eliovardo ; Mazumder, Madhulika ; Zaveri, Aryan ; Giovine, Raynald ; Manche, Alexis ; Pati, Swapan K. ; Clément, Raphaële J. ; Senguttuvan, Premkumar ( August 2021 , Advanced Functional Materials)

   Vanadium multiredox‐based NASICON‐Na_zV_2−yM_y(PO₄)₃(3 ≤z ≤ 4; M = Al³⁺, Cr³⁺, and Mn²⁺) cathodes are particularly attractive for Na‐ion battery applications due to their high Na insertion voltage (>3.5 V vs Na⁺/Na⁰), reversible storage capacity (≈150 mA h g⁻¹), and rate performance. However, their practical application is hindered by rapid capacity fade due to bulk structural rearrangements at high potentials involving complex redox and local structural changes. To decouple these factors, a series of Mg²⁺‐substituted Na_3+yV_2−yMg_y(PO₄)₃(0 ≤y ≤ 1) cathodes is studied for which the only redox‐active species is vanadium. While X‐ray diffraction (XRD) confirms the formation of solid solutions between they = 0 and 1 end members, X‐ray absorption spectroscopy and solid‐state nuclear magnetic resonance reveal a complex evolution of the local structure upon progressive Mg²⁺substitution for V³⁺. Concurrently, the intercalation voltage rises from 3.35 to 3.45 V, due to increasingly more ionic VO bonds, and the sodium (de)intercalation mechanism transitions from a two‐phase fory ≤ 0.5 to a solid solution process fory ≥ 0.5, as confirmed by in operando XRD, while Na‐ion diffusion kinetics follow a nonlinear trend across the compositional series.

    

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